Package org.apache.commons.rng.sampling

Class PermutationSampler

java.lang.Object
org.apache.commons.rng.sampling.PermutationSampler
public class PermutationSampler
extends java.lang.Object
Class for representing permutations of a sequence of integers.

Sampling uses UniformRandomProvider.nextInt(int).

This class also contains utilities for shuffling an int[] array in-place.

  • Constructor Summary

    Constructors 
    Constructor Description
    PermutationSampler​(UniformRandomProvider rng, int n, int k)
    Creates a generator of permutations.

  • Method Summary

    Modifier and Type Method Description
    static int[] natural​(int n)
    Creates an array representing the natural number n.
    int[] sample()  
    static void shuffle​(UniformRandomProvider rng, int[] list)
    Shuffles the entries of the given array.
    static void shuffle​(UniformRandomProvider rng, int[] list, int start, boolean towardHead)
    Shuffles the entries of the given array, using the Fisher-Yates algorithm.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • PermutationSampler

      public PermutationSampler​(UniformRandomProvider rng, int n, int k)
      Creates a generator of permutations.

      The sample() method will generate an integer array of length k whose entries are selected randomly, without repetition, from the integers 0, 1, ..., n-1 (inclusive). The returned array represents a permutation of n taken k.

      Parameters:
      rng - Generator of uniformly distributed random numbers.
      n - Domain of the permutation.
      k - Size of the permutation.
      Throws:
      java.lang.IllegalArgumentException - if n <= 0 or k <= 0 or k > n.

  • Method Details

    • sample

      public int[] sample()
      Returns:
      a random permutation.
      See Also:
      PermutationSampler(UniformRandomProvider,int,int)

    • shuffle

      public static void shuffle​(UniformRandomProvider rng, int[] list)
      Shuffles the entries of the given array.
      Parameters:
      rng - Random number generator.
      list - Array whose entries will be shuffled (in-place).
      See Also:
      shuffle(UniformRandomProvider,int[],int,boolean)

    • shuffle

      public static void shuffle​(UniformRandomProvider rng, int[] list, int start, boolean towardHead)
      Shuffles the entries of the given array, using the Fisher-Yates algorithm. The start and towardHead parameters select which part of the array is randomized and which is left untouched.

      Sampling uses UniformRandomProvider.nextInt(int).

      Parameters:
      rng - Random number generator.
      list - Array whose entries will be shuffled (in-place).
      start - Index at which shuffling begins.
      towardHead - Shuffling is performed for index positions between start and either the end (if false) or the beginning (if true) of the array.

    • natural

      public static int[] natural​(int n)
      Creates an array representing the natural number n.
      Parameters:
      n - Natural number.
      Returns:
      an array whose entries are the numbers 0, 1, ..., n-1. If n == 0, the returned array is empty.